Spring operated demolition device



E. F. CUTLER SPRING OPERATED DEMOLITION DEVICE A ril 4, 1967 5 Sheets$heet 1 Filed July 10, 1964 mm SN wm N? INVENTOR April 4, 1967 F. CUTLER 3,312,293

SPRING OPERATED DEMOLITION DEVICE Filed July 10, 1964 5 Sheets-Sheet Z FIG. 2

IN VENTOR.

EARL F. CUTLER BY A ril 4, 1967 v E. F. CUTLER SPRING OPERATED DEMOLITION DEVICE 5 Sheets-Sheet 5 Filed July 10, 1964 INVENTOR. EAQL F. CUTLER April 4, 1967 E. F. CUTLER SPRING OPERATED DEMOLITION DEVICE 5 Sheets-Sheet 4 Filed July 10, 1954 INVENTOR. E AQL F. CUTLER A ril 4, 1967 E. F. CUTLER 3,312,293

SPRING OPERATED DEMOLITION DEVICE Filed July 10, 1964 5 Sheets-Sheet 5 INVENTOR. 316 EAIZL FCUTLEIZ United States Patent Illinois Filed July 10, 1964, Ser. No. 381,870 10 Claims. (Cl. 173-119) My invention relates to methods and equipment for striking powerful blows of heavy impact and/ or penetrating power. Such work includes, among other items, the demolition of buildings of all sorts, especially brick and concrete, quarrying, and rupturing massive and recalcitrant masses of rock or masonry. The invention includes among its objects and advantages the striking of such blows at any desired point and in almost any desired direction, with greater force and follow-through of a higher magnitude than has heretofore been available, except in the case of large relatively stationary pile drivers.

In the accompanying drawings:

FIGURE 1 is a side elevation of equipment for practicing the invention;

FIGURE 2 is a section of the upper half of the ram roper;

FIGURE 3 is a similar section of the lower half of the same ram;

FIGURE 4 is a section on line 44 of FIGURE 3;

FIGURE 5 is a fragmentary longitudinal sectional view taken substantially along the line 55 of FIG- URE 2; v

FIGURE 6 is a longitudinal section indicating a different contact arrangement between the hammer and the tool;

FIGURE 7 is a detail section on line 77 of FIG- URE 6;

FIGURE 8 is a section similar to that of FIGURE 6 indicating the use of a plurality of small springs to replace the large spring of FIGURE 6;

FIGURE 8 is a section similar to that of FIGURE 6 indicating the use of a plurality of small springs to replace the large spring of FIGURE 6;

FIGURE 9 is a section on line 9-9 of FIGURE 8; and

FIGURE 10 is a section of another multiple spring construction.

In the embodiment of equipment selected to illustrate the invention the motor vehicle 10 is a well-known piece of equipment sold under the trademark Gradall. As these have been actively on the market for several years and their characteristics and capabilities are well-known, the description of the vehicle is limited to enumerating the characteristics that have some bearing on the use of the tool. It will be obvious that the same tool can be and frequently is mounted on any piece of mobile or stationary equipment.

The chassis 12 has front steering wheels 14 and is moved from place to place :by a power plant beside the cabin 16. The rear end, for heavy capacity work, is provided with four load-carrying wheels, a leading pair 18 and a trailing pair 20. The boom operator occupies the cubicle 22 which is also provided with a power plant at 24. The boom proper 26 is rotatable about its longitudinal axis in a supporting ring 28, with hydraulic power means for rotating it and holding it in any desired position. An extension 30 i slideably mounted in the boom 26 and may project to different distances, with its axial movement controlled by conventional hydraulic cylinders not illustrated. The outer end of the boom is provided with a main pivot 32 and a crank arm 34 which may be rotated around the pivot 32 by hydraulic pressure means acting in either direction along the line of the arrow 36.

The ram comprises the .main spring housing 38 and the power drive 40 and a hydraulic power unit 42 op- 3,312,293 Patented Apr. 4, 1967 erated by compressed oil from the power plant 24. The main housing 38 ha spaced flanges 44 extending out to engage the pivot 32. It will be obvious that the ram can be rotated a substantial" distance in either direction from the position illustrated around the pivot 32, and the entire assembly of the boom 26, extension 30 and ram can :be rotated around the axis of the boom to have the ram extend horizontally and strike a blow sidewise or to turn it so that it strikes in an upward direction.

The striking tool 46 has limited axial sliding movement in housing 38, which housing encloses a compression spring 48 and a heavy hammer '62, see FIGURES 2 and 3. In the large size unit the tool weighs about 175 pounds and the hamer weighs about 450 pounds and the spring exerts a force of 10,000 pounds when fully compressed. The maximum stroke for the hammer is about 9" and the footpounds of energy delivered on each blow are approximately 4300.

The transmission of striking blows Referring now to FIGURES 2 and 3 the housing 38 encloses a compression spring 48. The upper end of the spring bears against a seat 50 which is separated from the unyielding end member 52 by a thin cushion 54 of urethane plastic.

At its lower end the spring 48 bears on a companion seat 56 which is also separated from the annular pusher ring 58 by a urethane gasket 60.

The rnain mass of the striking hammer is a long rod 62 coaxial with the spring and extending up to the power drive above the spring and having a striking head 64. At the rear of the striking head an annular flange 66 receives the force of the spring transmitted through the collar 58.

. The tool 46 is slideable in a long bearing 68 in a hous- 7 mg extension 70 attached, as by suitable bolts 72, to a.

flange 7 4 integral with the housing 38.

In the inactive, or rest, position illustrated in FIG- URE 3 the spring is 1" shorter than its uncompressed length and is delivering a thousand pounds to the collar 58, which rides on a steel follower ring 76. The follower 76 rides on a thick gasket 78 of special rubber much stiffer and stronger than the tread of a motor car tire and identi-- fied in the trade as durorneter No. 9 rubber. The gasket 78 rides directly on the rigid lower end 80 at the bottom of the housing 38. The hammer head 64 slides in the ring 76 and ha a slight clearance at 82 where it passes through the housing bottom 80.

The upper end of the tool 46 carries a cup 84 having a relatively thin cylindrical well 86 in which is positioned first a cushion 88 of urethane plastic and second, a brass plug 90. When a blow is struck the impact of the head 64 is delivered to the plug 90, which expands under the hammering and anchors itself firmly in the well.

a few thousandths of an inch so that this expansion will anchor everything firmly in place. Above the cylindrical well portion 86, the wall of the well 86 is continued in a cone 92 of very slight outward inclination. The top of the cone 92 exceeds the diameter of the hammer head 64 enough to eliminate any possibility of impact other than along the acute angle of the interior wall of the cone 92. On the downstroke, it also, for a hundredth of a second or so, has enough air pocketed under the head 64 so that the escape of the air around the narrow peripheral orifice remaining between the cone 92 and the head 64 involves a substantial pressure and materially reduces the instantaneousness of the metal to metal impact.

Means are provided for preventing rotation of the tool with respect to the housing 38. The extension 70 has outwardly projecting flanges 94 in spaced pairs and the cup has a heavy upper lip 95 notched at 96 to receive I .prefer to provide the well with a very slight reverse taper of square guide rods 98 fastened between the flanges 95. Four such guide rods are provided, equally spaced around the periphery.

In the position of FIGURES 2 and 3, with the hammer head 64 in lowered position, the minimum tension of a thousand pounds in the spring 48 is carried by the washer 78 abutting the housing bottom 80. The 175 pounds of hammer weight holds the hammer in the position shown with the lip 95 resting on another durometer No. 9 rubber gasket 102. There is a slight clearance at 103 under the end of the head 64, to avoid letting the hammer blow injure the housing 70.

Now, when the tool 46 is forced axially upward by engagement withthe work, the tool immediately moves up to close the clearance at 103, and then in unison with the hammer 64 a distance of 2% inches until the lip 95 is abutment with a steel ring 104. Further upward movement of the tool with respect to the casing is positively prevented by the hard rubber gasket 106, which abuts the bottom of the bottom housing ring 80.

At this point the load on the point of the tool can immediately rise to the weight of the tool itself, which is about 175 pounds, and the weight of the entire ram, which totals about 2800 pounds. If, now, the operator uses the hydraulic controls for the boom 26 to move the boom lower, additional weight up to the capacity of the boom and its hydraulic equipment can be imposed on the tool without any additional effect on the spring.

It will be noted that the cab 22 and its power plant 24 are on a small platform 103 and this platform is rotatable around the axis of a conventional kingpin indicated at 110. Thus an extra two tons or so of downward force can be exerted by the hydraulic mechanism through the boom 26, to the extent of rocking the cab back on the kingpin 110 and exerting a decided lift on the rear end of the motor vehicle.

Since there is a material leverage ratio of about 2 to 1 :between the upward force on the tool 46 and its lever arm around the front wheels 14 compared with the leverage of the rear wheels, it is not impossible to lift the wheels 18 and 20' clear of the ground, but this would be an extreme condition of operation. But without lifting the rear wheels, the tires in the front wheels 14 are compressed an inch or so with a corresponding rise in the wheels 18 and 20, although their tires still have some hearing on the ground. This enables the operator to put any desired weight from 175 pounds up to as much as tons or more, on the point of the tool before any blow is struck.

With any dynamic pre-loading within the limits indicated, the operator may now operate the power transmission to withdraw the hammer to the end of its upward movement, at which time the spring 48 is suddenly released, and the hammer starts down with about 10,000 pounds pushing on it. This spring pressure will have decreased to about 3750 pounds at the time the hammer strikes the tool, but that 3750 pounds remains active during the movement of the tool into the material to be ruptured. Furthermore, the effective mass providing abutment and inertia to prevent the force generated at the point of the tool when the blow is struck from causing a reverse movement of the ram, includes2800 pounds of the ram itself and an additional mass of the same order of magnitude in the boom and a substantial fraction of the mass of the entire body of the motor vehicle.

Any upward movement at the end of the boom, reduces the load on wheels 18 and 20 and increases the load on wheels 14, and lowers the front end of the vehicle. The effective resistance of the running gear to this displacement can be more than doubled, if desired, by placing a conventional outrigger jack 107 under the front bumper 9, and lifting the bumper 109, two inches or so. This gives an equilibrium with four wheels, 18 and 20, at the rear, and the unyielding jack 107 at the front. Any upward displacement of the boom now results in reduction of lift by all four rear wheels around a remote fulcrum at 107, as distinguished from rotating the vehicle body around a point about /3 of the way forward from the rear support, with downward movement of the front end at 109.

Power drive As best indicated in FIGURE 2 and FIGURE 5 the rod 62 carries near its upper end a crosshead presenting downwardly facing abutments 122 on opposite sides and the twin bull gears 124- and 126 each carry two rollers 128 spaced 180 apart on opposite sides of the axis of rotation. As best indicated in FiGURE 2 one such roller is indicated at 128a making its initial contact with the lower surface of its abutment or track.

As the roller moves up to position 12% it rolls to and fro on the under surface of the track and position 128b is just before release. When the contact between the roller and its track has moved to the point identified as 130 the pressure of the roller will come to pass through the axis of rotation at 132 and the load on the motor becomes zero. Thereafter during a rotation of the bull wheel that amounts to less than one radius of the roller, the track, being forced down by the heavily compressed spring, will push the roller strongly in the direction of rotation, but there is no runaway movement of these parts because the bull wheels are driven by a countershaft 133 through a worm 134 or other irreversible transmission. The momentary absence of load when this occurs is evidenced by a tiny convulsive movement of the flexible hoses carrying the high pressure oil to the drive motor that turns the worm.

The force of the spring is maximum at release but at release the linkage is not far from dead center so that movement is very small, and as the rollers clear the ends of the tracks on both sides at the same time, the release has been found to be quite durable and dependable.

The thousand pound load on the spring when at rest has been found necessary because if a large spring under heavy stress is allowed to go to zero stress repeatedly it will crystallize and rupture, but it can move from one thousand pounds compression to ten thousand and back indefinitely without metallurgical deterioration.

Although the live dynamic pre-load of the spring set up by moving the hammer and tool up 2% inches by pushing down on the tool shortens the distance the hammer travels before impact by only a little less than /3, that final third of the hammer stroke represents much less than /3 of the total spring energy because it is the third where the spring force is least. The additional load imposed on the tool by the boom before the blow is struck, is limited in amount only by the weight and strength of the boom and the vehicle. It has been found that different types of material respond best to Widely varying amounts of boom load, with massive granite and reinforced concrete structures calling for maximum boom load and easily fracturing materials such as obsidian at the other end of the scale giving best response to almost no boom load at all, 1

It has been found that with objects and materials of different degrees of resistance to the entry of the tool, only a little practice by the operator is needed to enable him to adjust the pre-load from blow to blow to the amount of force that experience shows gives the maximum'eifect on the material to be ruptured.

Methods of operation The parts are preferably designed and proportioned so that the spring load between the tool and the frame,

spring force available on the hammer when it is fully retracted. The operator now has at his disposal a substantial variety of modes of operation, adaptable to the different types of objects to be ruptured.

For instance, using approximate actual working values for clarity, the tool may have a spring load of /2 ton with respect to the frame when in its advanced position. Movement of the tool back to the rear end of its limited stroke may increase the spring load to 2 tons, and this movement moves the hammer also. The maximum force available with the hammer withdrawn from the tool to the rear end of the hammer stroke is 5 tons, and the withdrawn hammer is about 6 inches away from the tool.

Where the object to be ruptured is of sufficient structural strength to carry a static load on the point of the tool up to more than 2 tons, the dynamic pre-load that may be imposed is limited only by the weight available and the structural strength of the frame and the boom and the vehicle.

Thus, the operator can, and in practical experience not infrequently does, advance the vehicle and boom toward the object to be ruptured, with force that moves the tool back to the end of its stroke at 2 tons, and then adds another 2 tons. With such a vehicle as a heavy, motor vehicle, the entire operating unit may carry substantially its entire weight at the remote end of the vehicle and the point of the tool, in which case the other end of the vehicle is relieved of load,

With such a dynamic pre-load value on the work, retraction of the hammer occurs without perceptible displacement of any other parts. Then when the spring is released, for one hundredth of a second or so, the high acceleration of the hammer under the 5 tons of spring force will partially relieve the dynamic pre-load on the point. This also will ordinarily not result in any noticeable displacement of any of the other parts, although it reduces the contact force between tool and work before impact occurs.

At the instant the hammer meets the tool, the spring will still be lifting the frame with a force of 2 tons and the full dynamic pre-load will be back on the point of the tool, still with no noticeable displacement of any part except the hammer and spring.

During this free stroke of the hammer, the mass in which the spring energy is stored is the hammer itself, weighing about 450 pounds, and at the instant of impact with the anvil, the moving mass is increased by the weight of the tool, and a combined weight of about 650 pounds, with some 4000 odd foot-pounds of kinetic energy, carries the point of the tool into the work.

At the moment of impact, the spring is still contributing 2 tons to the pressure of the point against the work. To this propelling force is added, in a time interval that is probably less than one-thousandth of a second, a mo-- mentary shock force which is of maximum value not definitely ascertainable with ease, but which may well be 100 tens or 1000 tons, depending on the structural strength of the material at the precise point where the hammer point is pushing.

To the extent that the tool penetrates the object, the peak of shock force is reduced. For instance, if the blow carried the tool into the object 1 inch, at the end of the stroke the frame and boom will move down 1 inch together and the boom and vehicle will reinstate the original dynamic pre-load force preparatory to the next blow, but the 4000 footpounds were used up in a travel of one inch. If the work is more recalcitrant, and the tool only progresses inch, the average force during the movement will be four times as great. But in either instance the peak force during the tool movement remains a matter of conjecture.

Going to the opposite extreme, it will be obvious that if the object is incapable -of sustaining the tool point, with a load of only one-half ton, the tool will simply meet the work and continue its movement and the work will crumple before it.

The entire gamut between these two extremes is within the field of practical experience with such a tool. For instance, where the object can sustain a load of only 2 tons, the operator may choose to impose more than that and simply push through, or he may set up a dynamic pre-load of only one ton and deliver a blow, to get greater fragmentation of the object, as distinguished from mere penetration or displacement. When the operator sets up a dynamic pre-l-oad between about /2 and 2 tons, the tool will float at an intermediate point in its own stroke until the hammer arrives.

With any pre-load, the repeated strokes will have a stroke frequency lower than the vibration frequency of the frame and boom and vehicle, with respect to the contact between the vehicle and the ground. Common frequencies are from 40 to blows per minute. Thus the entire unitary structure of vehicle, boom, and frame, may oscillate in approximate synchronism with each stroke of the hammer. The frame and boom will move down together after each impact, by the distance the tool moved on the blow. The weight and the inertia of the entire unit contributes to the follow-through of the tool point until the tool is stopped, and the original dynamic preload on the point is restored a material fraction of a second before the next impact occurs, ready for the next assist from the hammer.

Because the tool point is never allowed to separate or bounce on the work, there is never any opportunity for either large or small fragments of the work to be dis placed into a cavity at the point of the tool, and get pulverized by the next blow into a powdery mass that distributes the energy of the next blow into a larger volume. An initial dynamic pre-load of, say 3 tons, shoots up almost instantaneously at the moment of impact, and then subsides, but only back to about 3 tons, and not back to, or even near to, zero.

Very sharp, shattering blows The contacts between the hammer and the tool indicated.

in FIGURE 3 cushion the time during which the tool itself gets up to the same speed as the hammer, over a time interval that can be very roughly estimated at something like 50 nanoseconds or' so. Such tools are used to work on and in soft shale, baked mud, reinforced concrete, granite, limestone, and a wide variety of other materials. Certain materials shatter more readily when the blow is extremely sharp at the point where the material itself receives the impact. For such materials it is advantageous to have a much closer approximation to the contact between the tool and the material which would occur if the tool and hammer moved together throughout the entire hammer stroke and the tool was in movement at the time the material encountered it.

Referring to FIGURES 6 and 7, the hammer shaft 202 corresponds to the hammer shaft 62 of FIGURES 2 and 3, so far as its action on the tool is concerned. It is indicated as activated by the same spring 48 as in FIGURE 2, riding on the metal seat 204 which transmits thethrust to the gasket 206. The hammer head that delivers the thrust to the tool 208 is a flat faced disc 210 of maximum The effectiveness of the instantaneous contact has been.

ascertained in practical use, but a minor incidental effect when using the transmission of FIGURES 2 and 5 was.

encountered, in that in the shaft 202 the instantaneous contact set up supersonic vibrations of unknown frequency, but which might well be anything from 30,000 to 60,000 cycles/sec. The material of the one piece unit comprising shaft 202 and head 210 is capable of functioning without deterioration for an indefinite life so far as the consequences of such vibration are concerned. The tool 208 may or may not experience similar vibrations, but if it does, it is capable of enduring indefinitely. But after a relatively short period of use the nut at the top of the shaft of FIGURE 2 would recrystallize and disintegrate as a result of the heavy vibrations imposed on it.

After several unsuccessful attempts to prevent this, the construction of FIGURE 6 was found to be satisfactory. The shaft 202 extends only about /3 of the length of shaft 62 of FIGURE 2 and near its upper end it has a doughnut-like bulge at 219. A continuation shaft 220 of identical diameter is provided with a similar bulge 222. The two parts are then positioned as indicated in FIGURE 6 with a slight axial gap, and clamped between two clamping shell members, each subtending a few degrees less than 180 around the axis of the shaft. These parts are machined with annular cavities accurately fitting the bulges 222 and 219, leaving an appreciable clearance at 224 to permit pressure on the clamp shells to be borne entirely by the shafts. The preferred pressure means is a one piece sleeve 226 machined with a taper of about /8" to the foot and forced into the assembled position of FIGURE 6 in a press exerting several tons of axial force.

Such a shaft, actuated at its upper end by the identical mechanism illustrated in FIGURES 2 and appears on practical test to be immune to deterioration due to vibration.

One possible explanation of this fact is that the natural period of supersonic vibration of the shaft portion 202 will not be the same as the natural period for the shaft 220 because they differ in length and weight. Similarly, the force of the supersonic vibration has to pass from the bulge 219 into the shell segments 221, and those segments, in transmitting any such vibration from bulge 219 to bulge 222, would have an entirely different natural frequency not the same as the frequency of part 202 or part 220. Whether or not this is the correct explanation, the fact can be stated based on extensive practical experience that the shaft of FIGURE 6, combined with the power transmission of FIGURE 2 has indefinite life so far as disintegration is concerned.

Suitable means are provided for limiting the rearward movement of the tool under preload before the blow. I have indicated a collar 207 fast on the tool 208, and a cushioning gasket 209.

Multiple springs For large size equipment and heavy loads the spring 48 is an abnormally large and heavy unit and does not lend itself readily to the best heat treatment or to convenient fabrication and installation. In FIGURES 8 and 9 I have indicated the same shaft element, 220 or 62 as the case may be, associated with a pressure receiving plate 302. The housing bottom plate 304 corresponds to the bottom 52 of FIGURE 2 but at one point it is provided with a circular aperture at 306 to receive a hydraulic motor 308 receiving power in high pressure oil through a conduit 310 and returning the oil at low pressure through the return conduit 312. As such motors are well known in the art and are in general identical with the motor 42 of FIGURES 2 and 5, these details have not been included in this specification.

The compression load when the shaft 220 is lifted is divided and distributed to six compression springs comprising four full diameter springs 314 and two small diameter springs 318 nested inside two of the springs 314. The other two springs 314 are not associated with smaller nested springs to leave clearance in one of them for the insertion of the hydraulic motor 308. This makes a very compact unit and the forces exerted are symmetrical around the axis of the shaft 220. The motor 308 rotates 8 a drive shaft 320 which drives the worm gear transmission to the bull shaft 132.

The individual springs of FIGURE 8 are of much more conventional sizes and it is much easier to replace one when necessary, and they have a much longer working life than the spring 48 of FIGURE 6.

In FIGURE 10 I have indicated shorter spring assembly with a larger margin of safety. This comprises an inner helical spring 402 telescoped on the rod 62 and an outer helical spring 404 abutting the stationary seat 450 and partly telescoped outside, and radially spaced away from, the spring 402.

A floating connector cup 406 lies outside the upper end of spring 402 and inside the lower end of spring 404. This cup has a bottom 408 abutting the upper end of the spring 402, and an annular lip or rim 410 abutting the lower end of the spring 404.

To duplicate the force-displacement curve of spring 48 (which has an expanded length of 36", a contracted length of 26", and a working stroke of 9"), springs 402 and 404 each have a force constant of 2000 pounds per inch; and may have an expanded length of 24", a contracted length of 19" and a working stroke of 4 /2". This reduces the total percentage length change from 27.8% of the unstressed length for spring 48, to 20.8%, and the smaller percentage imposed on springs 402 and 404, is only 72% of the percentage imposed on spring 48.

With the metal carrying stresses that are close to critical values, this reduction contributes materially to the margin of safety and the life of the spring in service, but the total axial dimension required is reduced from 36" to about 29".

Others may readily adapt the invention for use under various conditions of service by employing one or more of the novel features disclosed or equivalents thereof. It should be understood that where terms such as upper, lower, upwardly and downwardly, are used herein and in the appended claims, such terms should be understood as referring to the power hammer of the present invention when oriented vertically with the tool 46 pointed downwardly as shown for example in FIGURE 1.

As at present advised, with respect to the scope of my invention, I desire to claim the following subject matter:

1. A striking ram unit comprising, in operative association and combination: a frame; a striker moveable in said frame in a predetermined limited path; said path having an advanced end and a retracted end; resilient urging means normally urging said striker toward its advanced position; and power means for retracting said striker and loading said resilient means up to maximum load at fully retracted position; said resilient means comprising a proximate spring abutting said striker to push it in advance; a remote stationary fixed abutment in said frame; a remote spring resting against said remote abutment; said remote and proximate springs being telescoped one inside the other; an intermediate floating sleeve and cup telescoped outside one spring and inside the other spring; the bottom of said cup abutting one end of the inner spring; said cup having a lip extending radially outward at the end opposite its bottom; said lip abutting one end of said outer spring.

2. In a power hammer, the improvement comprising, in combination, a housing, a first stop member within said housing adjacent the lower end thereof and fixed relative to said housing, said first stop member having a central opening therein, a hammer shaft disposed within said housing and having a hammer head at the lower end thereof, said hammer head being movable through said opening in said first stop member, a compression spring located within said housing above said first stop member for urging said hammer head downwardly, said first stop member serving to limit the downward movement of the lower end of said spring, a tool-carrying anvil shaft having an anvil at its upper end for engagement by said hammer head, said anvil being disposed beneath said first stop member so that movement of said anvil and anvil shaft upwardly into said housing is also limited by said first stop member, and a second stop member spaced downwardly from said first stop member and fixed relative to said housing, said second stop member cooperating with said anvil so as to limit the downward movement of said anvil shaft relative to said housing.

3. The invention of claim 2 where said first stop member comprises an annular disc which is fixedly disposed within said housing and has a central aperture therein.

4. The invention of claim 3 where gasket means are provided, one on each side of said first stop member, one of said gasket means being disposed immediately above said first stop member to cushion the end of the blow of said hammer, and the other of said gasket means being disposed immediately belowsaid first stop member in order to cushion said anvil when the latter is limited in its upward movement by said first stop member.

5. In a power hammer of the type having a hammer shaft including a hammer head which is adapted to strike an anvil carried on one end of a tool-carrying anvil shaft in order to deliver a blow, including spring means for forcing said hammer shaft downwardly toward said anvil and means for retracting said hammer shaft against the force of said spring means after delivery of each blow, the improvement comprising, a housing, and a plurality of helical compression springs disposed within said housing and circumferentially spaced therein, each of said springs being parallel to said hammer shaft and having one end abutting against a fixed portion of said housing with its other end acting to urge said hammer shaft downwardly toward said anvil.

6. The invention of claim 5 including a hydraulic motor housed within one of said helical springs, and power drive means connecting said motor to said means for retracting said hammer.

7. The invention of claim 5 where at least one pair of oppositely disposed ones of said springs are compounded of an outer helical spring and an inner helical spring nested within said outer helical spring.

8. In a power hammer of the type having a hammer shaft including a hammer head which is adapted to strike an anvil carried on one end of a tool-carrying anvil shaft in order to deliver a blow, including spring means for forcing said hammer shaft downwardly toward said anvil and means for retracting said hammer shaft against the force of said spring means after delivery of each blow, the improvement comprising an improved hammer shaft including, incombination, a first cylindricah hammer shaft section having a hammer head at the lower end thereof, a second cylindrical hammer shaft section extending upwardly from the upper end of said first section, a first pair of radial locking means formed on the adjacent ends of said hammer shaft sections, a pair of oppositely disposed clamping members wrapped about the adjacent ends of said first and second shaft sections for joining the latter in spaced relation to one another, each of said clamping members having a second pair of radial locking means for cooperation with said first radial locking means, and means for holding said clamping members on said adjacent ends of said shaft sections.

9. The invention of claim 8 where one pair of said radial locking means comprises a pair of annular bulges each of which is generally semi-circular in cross section and the other pair of said radial locking means comprises a pair of annular recesses each of which is generally semi-circular in cross section.

10. The invention of claim 9 where said means for holding said clamping members comprises an internally tapered sleeve which fits over said clamping members.

References Cited by the Examiner UNITED STATES PATENTS 1,176,041 3/1916 Dunbar 173-15 1,267,174 5/1918 Bert 173123 1,356,556 10/1920 Payne 173119 1,891,221 12/1932 Cornett 173-44 2,796,856 6/ 1957 Gratzmuller 267--1 3,039,758 6/1962 Gratzmuller 2671 3,149,682 9/1964 Dunston 173-123 3,179,185 4/1965 OFarrell 173-133 3,244,241 4/1966 Ferwerda 173--105 FOREIGN PATENTS 206,253 7/ 1939 Switzerland.

FRED C. MATTERN, JR., Primary Examiner.

L. P. KESSLER, Assistant Examiner. 

5. IN A POWER HAMMER OF THE TYPE HAVING A HAMMER SHAFT INCLUDING A HAMMER HEAD WHICH IS ADAPTED TO STRIKE AN ANVIL CARRIED ON ONE END OF A TOOL-CARRYING ANVIL SHAFT IN ORDER TO DELIVER A BLOW, INCLUDING SPRING MEANS FOR FORCING SAID HAMMER SHAFT DOWNWARDLY TOWARD SAID ANVIL AND MEANS FOR RETRACTING SAID HAMMER SHAFT AGAINST THE FORCE OF SAID SPRING MEANS AFTER DELIVERY OF EACH BLOW, THE IMPROVEMENT COMPRISING, A HOUSING, AND A PLURALITY OF HELICAL COMPRESSION SPRINGS DISPOSED WITHIN SAID HOUSING AND CIRCUMFERENTIALLY SPACED THEREIN, EACH OF SAID SPRINGS BEING PARALLEL TO SAID HAMMER SHAFT AND HAVING ONE END ABUTTING AGAINST A FIXED PORTION OF SAID HOUSING WITH ITS OTHER END ACTING TO URGE SAID HAMMER SHAFT DOWNWARDLY TOWARD SAID ANVIL. 